Clamping and sequencing arrangement for vacuum printing frame



1967 D. T. BLATHERWICK 3,357,335

CLAMPING AND SEQUENCING ARRANGEMENT FOR VACUUM PRINTING FRAME Filed Feb.23, 1965 3 Sheets-Sheet 1 DeiberfT 'siafigev'wi k M Wa /1% fl-FroKUQELYJ Dec. 12, 1967 D. T. BLATHERWICK 3,357,335

' CLAMPING AND SEQUENCING ARRANGEMENT FOR VACUUM PRINTING FRAME 5Sheets-Sheet 2 Filed Feb. 25, 1965 I I w I a 0 I u I v m. w M? k .2 m Tm a 4 L o w aw Iw r 6 BM i 1% 5 w 1009 0 Z Z all am/w W w M :M ow vw ec.12, 1967 D. T. BLATHERWICK CLAMPING AND SEQUENCING ARRANGEMENT FORVACUUM PRINTING FRAME 5 Sheets-Sheet 5 QMW Filed Feb, 23, 1965 W De)barf T Blodfindick United States Patent 3,357,335 CLAMPING ANDSEQUENQING ARRANGEMENT FUR VACUUM PRINTHNG FRAME Delbert T. Blatherwick,Woodstock, Ill., assignor to American Photocopy Equipment (Iompany,Evanston, ill., a corporation of Illinois Filed Feb. 23, I965, Ser. No.434,455 13 Claims. (Cl. 5-76) ABSTRACT OF THE DISCLOSURE A vaccumprinting frame for graphic arts purposes swingable between thehorizontal and vertical positions having interlocked means for insuringthat operations take place semi-automatically in a desired sequence andincluding cover counterweighting means.

In the preparation of offset printing plates the plate and positive areinserted into a printing frame where they are held together under glassfor exposure to intense light. Vacuum is employed for forcing thecombined plate and positive into intimate contact with the glasssurface. The frame is swung from a horizontal loading position to avertical exposed position.

It is an object of the present invention to provide a novel clamping andsequencing arrangement for a vacuum printing frame which is positive andreliable and which enables plates to be exposed rapidly on a productionbasis with a minimum of care and attention on the part of the printingframe operator. In this connection it is an object to provide a clampingand sequencing arrangement which insures that the loading, evacuation,tilting and exposing sequence is carried out semi-automatically andconsistently from plate to plate reducing the possibility of spoiling aplate due to inadvertence or forgetfulness on the part of the operator.In this connection it is also an object to produce a printing frameclamping arrangement in which the frame once clamped cannot be unclampedwithout completing the operating cycle, i.e., without swinging the frameback into horizontal unloading position. Indeed, it is one of thefeatures of the present device that the vacuum is automatically releasedand the frame is automatically swung open upon restoration to horizontalposition.

It is another object of the present invention to provide a vacuumprinting frame and control arrangement therefor which is safe and whichovercomes the hazards to both the equipment and the operator which mightbe encountered in the operation of frames of more conventional type.

It is still. another object of the invention to provide a clamping andsequencing mechanism which includes a novel interlock arrangement whichcannot be defeated or overpowered by the machine operator and which iscapable of withstanding long hard usage under production conditionswithout maintenance or adjustment.

Other objects and advantages of the invention will become apparent uponreading the attached detailed description and upon reference to thedrawings in which:

FIGURE 1 is a perspective view of a printing frame apparatus constructedin accordance with the present invention.

FIG. 2 is a side view of the printing frame proper, unclamped and openin readiness for loading but with the wall of the frame partly brokenaway to reveal the internal details.

FIG. 3 is a fragmentary perspective of the mechanism shown in FIG. 2.

FIG. 4 is a fragmentary section looking along the line 4-4 in FIG. 3.

3,357,335 Patented Dec. 12, 1967 FIG. 5 is a fragmentary section lookingalong line 5-5 in FIG. 1.

FIG. 6 is a fragmentary section looking along line 66 in FIG. 3.

FIG. 7 is an enlarged fragmentary section corresponding to a portion ofFIG. 2.

FIG. 8 is a side View of the clamping frame similar to FIG. 2 butshowing the frame in closed and clamped condition in readiness forswinging to the vertical exposing position.

FIG. 9 is a fragmentary view of the rear portion of the mechanism at thebeginning of swinging movement.

FIG. 10 is a fragmentary view similar to FIG. 9 but showing the liftingof the rear latch which occurs upon restoring the frame to horizontalposition.

While the invention has been described in connection with a preferredembodiment, it will be understood that the invention is not limited tosuch embodiment and that I intend to cover the various alternative andequivalent arrangements which are included within the spirit and scopeof the appended claims.

Turning now to the drawings, FIGURE 1 shows a vacuum printing frameapparatus having a frame or housing 10 which includes a pair of spacedsupports 11, 12. Mounted between the spaced supports is a printing frame15 having a base portion 16 and a glass cover 17, the cover being hingedto the base portion by a hinge 18 at the rear edge. The cover isprovided with a handle 19 for swinging the cover upwardly, i.e., to openthe frame when thefrarne is horizontal.

For the purpose of supporting the frame 15 for swinging movement betweenthe horizontal loading position and the vertical exposing positions,shown dotted in FIG. 2, a transverse shaft 20 is provided at theunderside of the base portion in a substantially centered position,projecting at each side to form trunnions 21, which are seated inbrackets 23, secured to the supports 11, 12. The brackets constitute asimplified form of journal bearings and, being open at the top, permitthe frame 15 to be unstepped for easy removal when removal becomesnecessary.

Prior to discussing the clamping and sequencing arrangement forming thesubstance of the present invention, it will be helpful to have in mindthe internal construction of the printing frame. For the purpose ofsealing the cover to the base a peripheral gasket 30 (FIG. 5) isprovided surrounding a blanket 31 formed of rubber or the like coveredwith small protuberances 32. When the glass cover is seated on thegasket the blanket defines an evacuated space 33 which communicatesthrough a vacuum line 34 to a vacuum pump 35 which has a motor 37 underthe control of a switch 36. It will be apparent that when the vacuumpump is turned on air is withdrawn through the line 34 forming a vacuumin the space 33 and causing the blanket to be powerfully attractedtoward the glass cover plate. Thus during normal use of the device anunexposed plate and positive are placed upon the blanket and when thecover is closed and clamped, application of the vacuum causes theblanket to press the pair plate and positive against the surface of thecover thereby insuring a sharp image when the frame is subsequentlyrocked into vertical position and exposed to a high inten sity lightsource. The light source, which may, for example, be in the form ofmercury vapor lamps, is mounted in the rear portion of the housing 10and does not form a part of the present invention. The vertical positionof the frame is defined by suitable stops 33 formed by the supportingmembers II, 12 while the horizontal position for the frame may bedefined by stops 39.

In accordance with the present invention means are provided movable intoalternate positions for locking the base member 16 of the frame inhorizontal position during loading and for clamping the cover onto thebase, with the locking means being automatically released incident tothe clamping so that the frame is then free to swing upwardly toward itsexposing position. Thus I provide along the sides of the base portionclamping bars mounted for endwise reciprocating movement engaging aclamp at the forward end and a horizontal lock at the rear end. In thediscussion which follows attention will be given to the mechanism alongone side of the base portion, the near side as shown at FIGS. 1 and 2,and it will be understood that the mechanism is duplicated at both sidesof the frame. The clamping bar, indicated at 40 in the drawings, issupported in pairs of guide rollers 41 at the front of the frame and 42at the rear. The rollers are secured to plates mounted on the base 16 byscrews 43. Each roller is grooved so that the bar 40 is held captive.For clamping the cover when the clamping bar 40 is in its forwardposition, a clamping plate 50 is secured to the cover by screws 51. Atits lower end the clamping plate carries a roller 52 on a pin 53, theroller being preferably in the form of an antifriction. bearing having acircular outer race.

When the cover is separated from the base, forward movement of the bar40 is prevented by a front lock 55 in the form of an arm which ispivoted at 56 and biased upwardly against a stop 57 by a spring 58 intoobstructing position. When the cover is lowered (FIG. 7), the roller 52,engaging the lock 55, moves it downwardly out of the way of the bar 40so that the bar 40 is free to move forwardly into the clamping positionshown in. FIG. 8 in which the front end of the bar overlies the roller52.

For applying forward. clamping movement to the bar 40, a manualoperating lever 60 is provided at the center of the base having a shaft61 which extends the width of the base and which. terminates, in themechanism under discussion, in an arm 62. Arranged in the path ofmovement of the arm 62 is a roller 65 mounted on a pin 66 with theroller being spaced outwardly from the bar sufficiently to clear theguide 41. It will be apparent, then, that downward swinging movement ofthe manual lever 60 causes the arm 62 to engage the roller 65 to producethe desired clamping movement of the bar.

For the purpose of locking the frame in horizontal position when the bar40 is moved rearwardly, a stop member 70 is provided on the supportingstructure in position to obstruct downward movement of the rear end ofthe bar as shown in FIG. 2. For the purpose of engaging the stop member70, a roller 72 is secured to the bar by a pin 71. The dimensions andclearances are such, as shown in the drawings, that the bar 40 performseither the horizontal locking function (FIG. 2) or a clamping function(FIG. 8) and since the same member performs both functions,

positive interlocking of the functions is assured.

In accordance with one of the important aspects of the present inventionmeans are provided for maintaining the bar 40 in its clamping positionduring upward swinging movement of the frame and for causing the bar tomove to a clamp-freeing position when the frame is restored tohorizontal position. To accomplish this, the bar 40 is biased intoclamp-freeing position by a coil spring 80 which is secured to one end81 to the bar and at the other end 82 to the frame or housing, with alatch and arcuate track being provided at the rear end of the bar forholding the bar, against the force of bias, in the clamping position.Thus referring to the drawings, I employ a latch 90 pivoted to the framefor rocking movement about a pivot pin 91 and having an end face 92arranged in the path of movement of the roller 72 secured to the bar.The latch 90 is downwardly biased into the position shown in FIG. 9resting, in active position, on the stop 70. Arranged adjacent the stopsurface 92 of the latch and in the path of movement of the roller 72 isan accurate stop member 95 secured to the support or housing 10 andhaving a surface 96 concentric with the supporting trunnion 21 on thebase portion of the frame. In carrying out the in 4. vention the stopsurface 92 at the end of the latch is preferably overhanging, i.e.,offset from, the surface 96 so that when the roller 72 on the barcompletes its cycle, i.e., when the frame is restored to horizontalposition, the latch is engaged by the roller causing the latch to becrowded upwardly into a non-engaging position, enabling the roller 72 toslide under the latch and enabling the clamping bar 40 to be restored toa non-clamping position by the spring 80. Such latch movement isutilized to switch off the switch 36 which controls the vacuum pump sothat vacuum is released permitting the cover member 17 of the frame tobe raised relative to the base.

In accordance with one of the more detailed features of the presentinvention, the cover 17 is provided with a counterweight so that whenthe clamp mechanism, and vacuum, are released, the cover 17 swingsautomatically into open position. Counterweighting is, in the presentinstance, achieved by springs 100 acting on plates 101 pivoted at 102the springs being reactively connected to the supporting frame as shownin FIG. 1. Each plate has two rollers 103 and 104 spaced to act inopposition on a bar 107 pivotally connected to the cover 17 at a pin 106which is located forwardly of the trunnions 21 when. the base is inhorizontal position. Thus the springs 100 are not only capable ofopening the cover 17 with respect to the base but acts, when the coverand base are clamped together, to provide upward bias for the frame 15as a whole. In determining the force. of the springs 100, it ispreferably suflicient to raise the glass cover 17 against the forces ofweight and friction but excessive counterweighting is to be avoided. soas to reduce the damaging imp-act. At each side of the cover 17 is arubber bumper 105 provided in the path. of movement of the upper edge ofthe. cover for the purpose of absorbing minor impact without damage tothe cover when the cover is swung open. Under normal circumstances thebias simply services to start the upward movement of the cover and theoperator or the machine, grasping the handle 19 on the cover, guides thecover into its fully open position for removal of the positive andexposed plate.

It may be noted that the spring, has a large lever arm (the distancebetween the pins 102, 106) for supporting the cover while only a smalllever arm. (the radial distance from pin.10 6 to trunnions 21) biasingthe base and cover as a unit with respect to the supporting frameworkdue to the near center location of the trunnions.

Thus referring to FIG. 2, which shows the lever and spring assembly atthe near or right-hand side of the machine, the members. 101, 107, takentogether form a composite lever pivoted. on horizontal pivot pin 102secured to the outer frame or support. The lever arm at the input. sideof the lever is the perpendicular distance between the spring 100 andthe pivot 102 while the effective lever arm of the output side is theradial distance between the pivot 102 and the pin 106 at the end of thelever 107. Since the point of connection 106 is near the center ofgravity of the cover, the weight of the cover is assumed by the leversystem without any substantial amount of reaction force at, the coverhinge 18. The roller mounting for the lever arm 107, provided by rollers103, 104, permits the lever arm to accommodate itself to the varyingradius of the pin 106 with respect to the lever pivot 102, as the coveris opened and closed. When the cover is closed and clamped in place, thepivot pin 106, to which the biasing force is applied, lies closelyadjacent the axis of the trunnions 21 so that only a small amount ofspring biasing torque, if any, is applied to the frame as a whole. Sincethe trunnions 21 are, as shown, positioned near the center of theprinting frame, the weight of the frame is substantially balanced whenthe frame is horizontal, but since the trunnions are adjacent theforward face of the frame, the rearwardly overhanging com ponent ofweight, when the frame is approaching the vertical position, isefifective to apply final closing torque,

maintaining the frame seated in its closed position until intentionallytilted therefrom by the operator.

While the operation of the above described mechanism during a completeloading, exposing, and unloading cycle, will be apparent to one skilledin the art, it will be helpful, for the purpose of fully understandingthe manner in which the various functions are integrated, to consider atypical operating cycle, with reference particularly to FIGS. 2-10inclusive. It will be assumed that the frame is initially in horizontalposition with the cover upraised. Under such condition, as shown in FIG.2, the clamping bar 40 is in its retracted position under the urging ofthe biasing spring 80. The rear latch 90 is upraised and the roller 72on the clamping bar is blockingly supported on the stop member 70 whichis secured to the supporting frame of the machine. Forward movement ofthe clamping bar 40 is, under such circumstances, precluded since thefront latch 55 is in blocking position. Since the rear latch 90 isupraised, the vacuum pump switch 36, which is coupled to this latch, andwhich is of the normally closed variety, serves to keep the motor 37deenergized so that no vacuum is applied. Rocking movement of the frame15 forwardly beyond horizontal position is prevented by the fixed stop39 on the frame.

After the positive and unexposed plate are inserted into position on therubber blanket 31 in the base portion of the frame, the cover 17 ismanually lowered by the handle 19. Engagement between the roller 52 andthe clamping bracket 50 serves, first of all, to depress the front latch55 out of the way of the clamping bar 40. The manual clamping lever 60is then pushed downwardly by the operator causing the arm 62 thereof topress against the roller 65 on'the clamping bar forcing the clamping barforwardly into clamping position against the force of the biasing spring80. This moves the roller 72 from under the rear latch 90, enabling therear latch to drop into the position shown in FIG. 8 and releasing thecontrol switch '36 so'that the vacuum pump motor 37 is turned on.Application of vacuum through conduit 34 promptly evacuates the space 33above the blanket 31, causing the blanket to press the positive andunexposed plate intimately against the under surface of the glass cover.Because of the dropping of the rear latch 90 into obstructing relationwith respect to the roller 72 on the clamping bar, the clamping bar islocked in the clamped up condition in readiness for upward swinging ofthe printing frame. Moreover, the roller 72 at the rear end of the bar40is moved clear of the horizontal locking member 70 so that the frameis no longer locked in its horizontal position. Because ofthecounterbal'ancing effect of the springs light upward pressure applied tothe handle 19 by the machine operator suffices to swing the printingframe toward its vertical position. During the initial portion of thismovement the roller 72 on the clamping bar drops off the face of thelatch 90 onto the surface 96 of the curved rail 95 on the machine frame.Since the member 95 is concentric with the axis of swinging movement,the interference between the roller 72 and the curved member assuresthat the clamping bar dd remains in its forward or clamping positionduring the time that the printing frame is in transit between itshorizontal and vertical positions.

The capacity of the vacuum pump 35, as compared to the small volume 33above the blanket, is sufficient so that substantially completeevacuation of the space 33 occurs in an extremely short space of time, aspace of time which may be on the order of one second duration. Thisinsures that the positive and unexposed plate are clamped against theglass cover before the frame has had opportunity to move very farout ofits horizontal position. This insures that the positive and unexposedplate will have no opportunity to slip with respect to one another andinsures that the plate will be exposed with the positivein the sameposition as it was originally deposited. Thus there is no reliance uponthe operator to manually operate a switch for turning on the vacuumwhich runs the risk that the switch may be turned on too late so thatthe plate has an opportunity to slip out of position.

When the printing frame 15 strikes the fixed stop 37 which defines thevertical frame position, the light source is turned on. This may eitherbe done manually or automatically by a switch which is arranged in thepath of movement of the frame and actuated as the vertical stop surface37 is about to be engaged. The duration of the exposure may be eithercontrolled by the operator or may be controlled by an automatic exposuretimer and is a matter outside of the scope of the present invention.

Following exposure the machine operator, by grasping the'handle 19,pulls the printing frame 15 back toward its horizontal position. As theframe approaches the horizontal, the roller 72 strikes the corner of therear latch 9G by reason of the interference or overlap indicated at d(FIG. 8), raising the latch 90. Since the latch is thus moved out ofobstructing position with respect to the roller 72, the clamping bar 40moves rearwardly under the urging of the biasing spring so that theroller becomes supported on the horizontal locking member 70 locking theprinting frame in horizontal position. Simultaneously the switch 36,engaged by the upward movement of the latch 90, turns off the motor ofthe vacuum pump and releases the vacuum. With the clamping plate 50 andthe vacuum both released, the glass cover 17, is free to move upwardlyunder the influence of the bias provided by the springs 100. Theoperator continues the opening movement of the cover sufficient toremove the positive and exposed plate, This restores the mechanism tothe condition illustrated iii FIG. 2 and completes a single operatingcycle.

The function of the operator is thus reduced to the simple and naturalmovements of unloading, reloading, lowering the cover and clampingfollowed by upward swinging movement of the frame into verticalposition. The above mechanism insures that all of the steps required intheexposure of a platewill be carried out in a precisely predeterminedorder-without reliance upon the operators timing or judgment. Thisprecludes the possibility that an operator may spoil a plate-byperforming some function out of step as, for example, failing tomanually turn on the vacuum While the frame is still in itssubstantially horizontal position. Moreover, those motions which arerequired of an operator may be accomplished with light operating forcesso that the operator may run the machine over an entire work shift,unloading and reloading repeatedly on a production basis withoutfatigue. Movement of the cover and movement of the printing frame as awhole are both accomplished by using a single handle 19 on a cover.Since means are provided for locking the baseportion of the frame inhorizontal position, upward movement of the handle during the loadingcycle will have no effect upon the base portion. Conversely, with thecover clamped in place and the base portion released by its lock, upwardmovement of the handle produces bodily swinging of the frame. Theoperators efforts may be concentrated upon registering the plate andpositive and in either controlling, or overseeing, the exposure.

Moreover, the arrangement described above isfound to be safe and withoutrisk either to the machine or the operator. Thus the arrangement is tobe contrasted with prior devices in which it is possible for theoperator to swing the frame upwardly without clamping and withoutapplication of vacuum giving rise to the possibility that the cover maysuddenly swing free by reason of the biasing or counterbalancing forcewith resultant impact between the glass cover and the upper portion ofthe supporting structure, possibly resulting in breakage. I

In spite of the various interlocked functions performed by the presentmechanism, the'mechanism is inherently simple and. inexpensive, addinglittle to the cost of the total machine.

In the following claims the Words horizontal and vertical are to be'interpreted as "generally horizontal and generally vertical? The termglass refers to any transparent sheet material.

I claim as my invention:

1. In a vacuum printing frame apparatus the combination comprising a,pair of spaced supports,- a printing frame having a base portion andhaving a glass cover hinged at the rear edge thereof, means forcentral]? supporting the base portion on the supports for tiltingbetween a horizontal loading position and a vertical exposing position,stops on the supporting structure for defining said positions, clamps atthe forward edge of the base portion for clamping the glass cover into aseated vacuum-retaining position, clamping bars mounted for endwiseshifting movement along respective sides of the base portion foroperating, the clamps, a manual operator accessible at: the front edgeof the base portion for simultaneous shifting of the bars, means forlatching the bars in clamping position and for maintaining them inclamping position as the frame is tilted toward its vertical exposingposition, and means responsive to restoration of the frame to horizontalposition for releasing the latching means 2. In a vacuum printing, frameapparatus the combination comprisingv supporting structure including apair of spaced supports, a printing frame having a base portion and aglass cover hinged at the rear edge thereof, a connection for applyingvacuum above the base portion for urging a plate into seated engagementwith the glass cover when the cover is closed, means for centrallysupporting the base portion on the supports for tilting of the framebetween a horizontal loading position and a vertical exposing position,stops on the supporting structure. for defining said positions, a clampfor clamping the glass cover to the baseportion, means for locking theframe in its horizontal position, a manual operator for closing theclampand releasing the lock, means responsive to closing of the clampfor applying vacuum to the connection, means for biasing the cover intoits open position relative to the base portion, and means responsive torestoration of the frame to its horizontal position for simultaneouslyreleasing the vacuum and releasing the lock so that the cover begins toopen automatically upon restoration of the printing frame to horizontalposition,

3. In a vacuum printing frame apparatus the combination comprisingsupporting structure including a pair of spaced supports, a printingframe having a base portion and a glass. cover hinged at the rearedgethereof, means for centrally supporting the base plate on the supportsfor tilting the frame between a horizontal loading position and avertical exposing position, clamps at the forward corners of the baseportion for clamping the cover, clamping bars mounted for endwisesliding movement along the sides of the base portion and coupled to theclamps at their respective forward ends for clamping the cover when thebars are in a first limit position, means forming a locking surface onthe frame adjacent the rear end of the bars when the frame is in itshorizontal position for blockingly engaging the rear ends of the barsand for locking the frame in horizontal position when the bars are intheir opposite limit positions thus insuring that the clamps are clampedbefore the frame is swung from its horizontal position. v

4. -In a vacuum printing frame apparatus the combination comprisingsupporting structure including a pair of spaced supports, a printingframe having a base portion and a glass cover hinged at the rear edgethereof for sealthe base portion for clamping the cover, clamping barsmounted along the sides of the base portion for endwise sliding movementbetween first and second limit positions, said bars being coupled to theclamps at their respective forward ends for clamping the cover when thebars are in their first limit positions, means forming a locking surfaceon the frame adjacent the rear end of the bars when the frame is in itshorizontal position for blockingly engaging the rear ends of the barsand for locking the frame in horizontal position when the bars are intheir second limit positions, and means actuated upon moving the barsinto their first limit positions for evacuating the frame.

5, In a vacuum printing frame apparatus the combination comprisingsupporting structure including a pair of spaced supports, a printingframe having a base portion and a glass cover hinged at the rear edgethereof, means for centrally supporting the base portion on the supportsfor tilting between a horizontal loading position and a verticalexposing position, stops on the supporting structure for defining saidpositions, clamping means for the cover at the forward edge of the baseportion, means including a clamp operating member accessible for manualoperation at the front of the frame for moving the clamping means intoclamping position, means including a latch for maintaining the clampingmeans clamped up during the time that the frame is tilted. toward thevertical exposing position, and means responsive to the return of theframe to its horizontal position for releasing the latch for automaticrelease of the clamping means.

6. In a vacuum printing frame apparatus the combination comprising asupporting structure including a pair of spaced supports, a printingframe having a base portion and a glass coverhinged at the rear edgethereof, means for centrally supporting the base portion on the supportsfor tilting the frame between a horizontal loading position and avertical exposing position, stops on the supporting structure fordefining said positions, clamping means at the front edge of the baseportion for clamping the glass cover to the base, clamp operating meansincluding a manual control lever at the front of the base portion foroperating the clamping means, said clamp operating means having a latchfor retaining the same in a clamping position, means for tripping thelatch automatically incident to restoring the printing frame to itshorizontal position, and biasing means for urging the clamp operatingmeans into a non-clamping position so that the glass cover is unclampedautomatically upon tripping of the latch.

7. In a vacuum printing frame apparatus the combination comprising asupporting structure including a pair of spaced supports, a printingframe having aebase portion and a glass cover hinged at the rear edgethereof, means for centrally supporting the base portion on the supportsfor tilting the frame between -a horizontal loading position and avertical exposing position, stops on the supporting structure fordefining said positions, clamping means at the front edge of the baseportion for clamping the glass cover thereto, clamp operating meanscoupled to the clamping means and having a manual operating handle,means for keeping the clamping means engaged during the time that theprinting frame is tilted toward the vertical exposing position,

, means responsive to return of the frame to horizontal position forreleasing the clamping means, and means for biasing the glass covertoward the open position so that the cover opens automatically uponrestoring the frame to its horizontal position.

8. In a vacuum printing frame apparatus the combination comprising asupporting structure including a pair of spaced supports, a printingframe having a base portion and a glass cover hinged at the rear edgethereof, means for cent-rally supporting the base portion on thesupports for tilting the frame between a horizontal loading position anda vertical exposing position, stops on the supporting structure fordefining said positions, a clamp at the front edge of the base portionfor clamping the cover, locking means for holding the frame horizontal,manual means for simultaneously closing the clamp and releasing thelocking means so that the frame may be tilted away from its horizontalposition, and means responsive to return of the frame to horizontalposition for simultaneously releasing the clamp and resetting thelocking means, said glass cover being biased into open position foropening when the clamp is released.

9. In a vacuum printing apparatus the combination comprising supportingstructure including a pair of spaced supports, a printing frame having abase portion and a glass cover hinged at the rear edge thereof, meansfor centrally supporting the base portion on the support for tilting theframe between a horizontal loading position and a vertical exposingposition, stops on the supporting structure for defining said positions,a clamp at the forward edge of the base portion for clamping the coverthereto, means including a lock for holding the frame in the horizontalposition, manual means for simultaneously closing the clamp andreleasing the look so that the frame may be tilted from the horizontalposition, and means actuated upon release of the lock for applyingvacuum within the printing frame at a rate of evacuation which issufficiently great so as to insure clamping of the plate with respect tothe glass cover by the time that the frame may be swung substantiallyfrom its horizontal.

10. In a vacuum printing frame apparatus the combination comprisingsupporting structure including a pair of spaced supports, a printingframe having a base portion and a glass cover hinged at the rear edgethereof, a connection for applying vacuum above the base portion forurging a plate into seated engagement with the glass cover when thecover is closed, means for centrally supporting the base portion on thesupports for tilting the frame between a horizontal loading position anda vertical exposing position, stops on the supporting structure fordefining said positions, a clamp for clamping the glass cover to thebase portion, means including a lock for holding the frame in itshorizontal position, a manual operator for closing the clamp andreleasing the lock, means for disabling the manual operator until theglass cover is closed, means operated incident to closing of the clampfor applying vacuum to the connection, means for preventing opening ofthe clamp while the frame is swung from horizontal to vertical positionand back again, means for biasing the cover into its open position, andmeans responsive to restoration of the frame to its horizontal positionfor simultaneously releasing the vacuum and releasing the clamp so thatthe cover may be opened upon restoration of the printing frame tohorizontal position.

11. In a vacuum printing frame apparatus the com bination comprising asupporting structure including a pair of spaced supports, a printingframe having a base portion and a glass cover hinged at the rear edgethereof, means for centrally supporting the base portion on the supportsfor tilting of the frame between a horizontal loading position and avertical exposing position, stops on the supporting structure fordefining said positions, clamping means at the front edge of the baseportion for clamping the glass cover thereto, a handle on the glasscover, means for keeping the clamping means engaged during the time thatthe printing frame is tilted toward the vertical expo-sing position byupward force on the handle, and means responsive to return of the frameto horizontal position for releasing the clamping means so that upwardforce on the handle causes the cover to separate from the base portion.

12. In a printing frame apparatus the combination comprising asupporting frame including a pair of spaced supports, a printing framehaving a horizontal hinge connection adjacent the center thereof fortilting between a horizontal loading position and a vertical exposingposition, said printing frame consisting of a base portion and a glasscover substantially coextensive therewith, a second horizontal hingeconnection along the rear edge of the cover for hinging the same to therear edge of the base portion, clamping means for securing the cover tothe base, and biasing means connected to the center portion of the glasscover and reactively connected to the supporting frame for applying anupward biasing force to the center portion of the glass cover forbiasing the cover upwardly about the second hinge connection when thecover is free of the base while applying only limited bias to the frameas a whole about the first hinge connection.

13. A printing frame apparatus as claimed in claim 12 in which the meansfor applying biasing force to the cover is in the form of a lever havinga pivot fixedly positioned with respect to the supports together with abiasing spring for biasing the lever.

References Cited UNITED STATES PATENTS 7/1955 Padgett 76 8/1966 Benson95--76

1. IN A VACUUM PRINTING FRAME APPARATUS THE COMBINATION COMPRISING APAIR OF SPACES SUPPORTS, A PRINTING FRAME HAVING A BASE PORTIONF ANDHAVING A GLASS COVER HINGED AT THE REAR EDGE THEREOF, MEANS FORCENTRALLY SUPPORTING THE BASE PORTION OF THE SUPPORTS FOR TILTINGBETWEEN A HORIZONTAL LOADING POSITION AND A VERTICAL EXPOSING POSITION,STOPS ON THE SUPPORTING STRUCTURE FOR DEFINING SAID POSITIONS, CLAMPS ATTHE FORWARD EDGE OF THE BASE PORTION FOR CLAMPING THE GLASS COVER INTO ASEATED VACUUM-RETAINING CLAMPING BARS MOUNTED FOR ENDWISE SHIFTINGMOVEMENT ALONG RESPECTIVE SIDES OF THE BASE PORTION FOR OPERATING THECLAMPS, A MANUAL OPERATOR ACCESSIBLE AT THE FRONT EDGE OF THE BASEPORTION FOR SIMULTANEOUS SHIFTING OF THE BARS, MEANS FOR LATCHING THE